ansibleIntroduction to playbooks

Overview

In Ansible, a playbook is is a YAML file containing the definition of how a server should look. In a playbook you define what actions Ansible should take to get the server in the state you want. Only what you define gets done.

This is a basic Ansible playbook that installs git on every host belonging to the web group:

---
- name: Git installation
  hosts: web
  remote_user: root
  tasks: 
    - name: Install Git
      apt: name=git state=present

Playbook's structure

The format of a playbook is quite straightforward, but strict in terms of spacing and layout. A playbook consists of plays. A play is a combination of targets hosts and the tasks we want to apply on these hosts, so a drawing of a playbook is this:

Pictorial representation of an Ansible playbook

To execute this playbook, we simply run:

ansible-playbook -i hosts my_playbook.yml

Play's structure

Here’s a simple play:

- name: Configure webserver with git
  hosts: webserver
  become: true
  vars:
    package: git
  tasks:
    - name: install git
      apt: name={{ package }} state=present

As we said earlier, every play must contain:

  • A set of hosts to configure

  • A list of tasks to be executed on those hosts

Think of a play as the thing that connects hosts to tasks. In addition to specifying hosts and tasks, plays also support a number of optional settings. Two common ones are:

  • name: a comment that describes what the play is about. Ansible will print this out when the play starts to run
  • vars: a list of variables and values

Tags

Play contains several tasks, which can be tagged:

- name: Install applications
  hosts: all
  become: true
  tasks:
    - name: Install vim
      apt: name=vim state=present
      tags:
        - vim
    - name: Install screen 
      apt: name=screen state=present
      tags:
        - screen

Task with tag 'vim' will run when 'vim' is specified in tags. You can specify as many tags as you want. It is useful to use tags like 'install' or 'config'. Then you can run playbook with specifying tags or skip-tags. For

ansible-playbook my_playbook.yml --tags "tag1,tag2"
ansible-playbook my_playbook.yml --tags "tag2"
ansible-playbook my_playbook.yml --skip-tags "tag1"

By default Ansible run all tags